FC76DCU vs some sort of 80 ED

[IB20]

This is a great help https://www.telescopes-et-accessoires.fr/Files/131989/FS-60CB_instruction_manual_EN.pdf 

It comes with an aux ring TKP20001 in the optical train but the schematics shows that for straight-through visual, so needs removing with a diagonal in place.

Despite the really short draw-tube travel, I have been able to focus all my eyepieces with the Tak prism diagonal with the exception of the 13mm Delite, there’s a work around by moving it slightly higher in the diagonal though.

I know @JeremyS found an adapter combination to get a Lunt Wedge and Quark working too but I haven’t had chance to do any white light observing yet.

I think my next purchases for this are the 5XW Pentax and a micro-focuser, either the More Blue or MEF-3 upgrades.

 

[Fedele]

But Back focus is sufficent?

i have also a FTF2025 rready for the 76. 

I m thinking if it will go in focus with daystar Chromo, bino, etc

[IB20]

I haven’t found anything that takes too much outward travel so far. The Delite requires more inward focus. My understanding is the Herschel Lunt wedge is too little inward travel as well.

[Fedele]

i have the baader cool ceramic to

a maxbright 2

bino viwing with no goc id for me important

[Fedele]

i rewrite the post for more  more clarity.

I generally use the maxbright screwed directly to the Baader T2 32 prism and this with the 2 "nose. I have also the 2025. 

1) i want to reach focus with Baader Cool Cermaic 2" both in mono and in Bino with the maxbright. I hope that at least the first option is ok

2)  i want to reach focus with Maxbroight II for night visions and if possibile wit NO GPC

 

So...can you tell me: 

1) the measure of  back focus of the telescope from the  original focuser

2) from the tube (no original focuser)

[Fedele]

uhm...

i think i will return back to some other choice

Edited January 23, 2022 by Fedele

[HollyHound]

1 hour ago, Fedele said:

uhm...

i think i will return back to some other choice

Having never tried binoviewing, let alone using a wedge too, on my FC-76DCU, and given @Stucomments… it might be a risky choice for that purpose unfortunately ☹️

As a grab and go refractor for “normal” mono viewing, I still highly rate it 👍

Good luck with your choice 🤞

[IB20]

I don’t use binoviewers but it concerns me they seem quite impossible in this system. I’m annoyed that such an expensive piece of equipment isn’t perfect but then I remember even my £300 80mm achromat, with its 25cm of draw-tube travel, still struggled with in-focus.

[Robindonne]

Maybe a more modular design like a Borg for binoviewers?

[Fedele]

Someone is able to perform the calculation of back focus for the FC76 if i use the FTF2025BCR + A20-302??

[Fedele]

at least i need: 

 

1) the Back focus value from the 2" aperture of the fok

2) the measure of the original focuser

[Fedele]

8 hours ago, Stu said:

They are not impossible at all. Don’t forget the Baader CoolWedge needs quite a lot of back focus, much more than a normal diagonal or prism. Combining that with binoviewers and it becomes challenging for many scopes.

The thing is, lots of people fixate on it being essential to be able to use binoviewers without a barlow or GPC. I don’t see it like that. I prefer widefield views through a single eyepiece. Stars are, to my eye, just that bit purer and sharper and overall I prefer the views and don’t feel the need to binoview in these circumstances.

Where I see the benefit of binoviewers is for high power lunar, planetary and solar views. They make it much more relaxing to observe and, particularly for solar and lunar, enhance the views quite dramatically. They also reduce floater visibility in smaller refractors with tighter exit pupils. I still prefer cyclops views of double and multiple stars at high power because of the purity of the star images.

I don’t think I’ve tried the 76DCU at night with binoviewers and a T2 prism so will give that a go and see what happens.

thanks but this are your opinions.  i have not asked a lesson on Bino vs mono. i have asked measures.

For me Bino view is essential in every field. And this is not a point of discussion

If you like to obseve like Polifemo no problem... for sure it is not what  i ve asked

 

Edited January 24, 2022 by Fedele

[Fedele]

this is the Baader with maxbright 2 on original fok of the DL

nothing is impossible

 

i just want to know the optical real ( not metal/photographic) back focus measures

 

the rest are just calculations

[Fedele]

sTU...

in another post you show the setup with The Baader Cool Ceramic 2", a Bino and the FS60CB with the FTF 2025 FOK

So if work with the FS60CBU, why not with the fc76?  

1) can you try to mount the 2025 on the FC76 and check the same setup on it?

2) In fact, if it reaches the fire with the Baader cool ceramic, which is one of the accessories that most of all sucks back focus, why shouldn't I reach the fire with only the turret mounted in a T2 32 prsim?

Edited January 24, 2022 by Fedele

[Fedele]

I also take this opportunity to ask you another question.
You have both the FS60CB and the FC76DCU. The former is extremely smaller and lighter than the latter.
The former will be extremely more enjoyable to use as a grab and go.
What I ask you is: the performance of the 76 (especially on the moon, Sun and planets) is so much better than the 60 (obviously for the larger diameter but ...) that you prefer to take the FC76 most of the time?

[Fedele]

ccan you measure the original fok of the FC76DCU please???

i find this image. You know for sure that the FS60CBU and the FC76dcu HAVE THE SAME FOCUSER?
so i have in this image the measure of it

[Ricochet]

With the 76dcu, can you remove the smaller of the two OTA sections and screw the focuser directly to the longer front section? If this section can be removed and is the same as the one on the fs60 shown above, then removing the 127mm section of the OTA and adding a binoviewer with an optical path length of ~110mm should leave a telescope that focuses. Whether it is possible to balance the scope without the dovetail impeding the use of the focuser or whether the drawtube vignettes the image is another issue. 

[Fedele]

I've already done my math. With the appropriate accessories it is possible to use my Maxbright 2 without a GPU

[Stu]

2 minutes ago, Fedele said:

I've already done my math. With the appropriate accessories it is possible to use my Maxbright 2 without a GPU

My contributions clearly aren’t appreciated so I wish you good luck Fedele.